1. Field of the Invention
The present invention relates to methods of electroplating and to products made thereby. In another aspect, the present invention relates to methods of electroplating a conductive metal onto a substrate, and to products made thereby. In even another aspect, the present invention relates to methods of electroplating conductors onto a seed layer supported by a substrate, and to products made thereby. In still another aspect, the present invention relates to methods of electroplating conductors onto a seed layer supported by a diamond substrate, and to products made thereby.
2. Description of the Related Art
It is the physical and chemical properties of natural diamonds which render diamonds suitable for use in a wide range of applications. For example, natural diamonds are the hardest substance known and exhibit low friction and wear properties. Specifically, a natural diamond's thermal conductivity, thermal diffusivity properties, electrical resistivity and microhardness invite its substitution in various applications.
Specifically with respect to electronic applications, diamond, with a thermal conductivity four times that of copper and a dielectric constant less than alumina or aluminum nitride, has long been recognized as a desirable material for electronic substrates.
It is likewise believed that diamond films would find utility in a broad range of electronic uses.
Unfortunately, diamond films are not naturally occurring, but rather must be manufactured using any of a host of techniques.
Fortunately, however, the physical and chemical properties of synthetic diamond films have been found to be comparable to those of bulk diamond.
For example, it has been reported that electron assisted chemical vapor deposition films have electrical resistivities greater than 10.sup.13 .OMEGA.-cm, microhardness of about 10,000 HV, thermal conductivity of about 1100 W m.sup.-1 K.sup.-1, and thermal diffusivity of 200 to 300 mm.sup.2 /s. These compare favorably to those properties of natural diamond, i.e, resistivities in the range of 10.sup.7 to 10.sup.20 .OMEGA.-cm, microhardness in the range of 8,000 to 10,400 HV, thermal conductivity in the range of 900 to 2100 W m.sup.-1 K.sup.-1, and thermal diffusivity of 490 to 1150 mm.sup.2 /s. Thermal gravimetric analysis demonstrates the oxidation rates of diamond films in air are lower than those of natural diamond. Additionally, it is reported that the starting temperature of oxidation for microwave-assisted chemical vapor deposition diamond film is about 800.degree. C., as evidenced by weight loss, while the morphology shows visible oxidation etching pits at temperatures as low as 600.degree. C.
Thus, diamond films also show promise for finding utility in a multitude of applications, including electrical applications.
Currently, chemical vapor deposition diamond film has experienced limited market entry primarily as heat sinks for laser diodes. However, there are many other industrial uses planned for diamond film, virtually all of which require metallization.
For example, diamond film substrates have been hailed as the only solution to many of the thermal management problems currently encountered in the electronic and optoelectronics packaging area. As the packing density of electronic systems increases, this thermal management problem is only going to exacerbate. Metallization of diamond film substrates with highly conducting metals such as gold and copper is essential for these applications. Some of the applications which are in dire need of the development of a tenaciously adhering conducting metal film on a diamond substrate include laser diodes and diode arrays for telecommunications, power modules for on-board satellites, high powered microwave modules, MCMs, and especially 3-D MCMs.
However, while the industry is in dire need of a tenaciously adhering (&gt;1 Kpsi on peel test) electroplated conducting metal film on a diamond substrate, the chemical inertness of diamond resists the formation of adherent coatings on it. This is especially true for large area (&gt;1 mm.times.1 mm) diamond film substrates and thick metal films (&gt;2 microns).
Presently, metallization is accomplished through some form of physical vapor deposition. While this produces a high quality film, it also produces high material cost due to its extreme waste of metal. Electroplating is preferable because is allows metal to be deposited selectively, which would cut waste by over 90% from what is consumed in a physical vapor deposition process.
Physical vapor deposition processes are currently the industry standard because films deposited by such processes tend not to blister or peel at high temperatures. In a physical vapor deposition process, the substrate is mounted inside a high vacuum chamber. The chamber is evacuated, and metal is either evaporated or sputtered to form a coating on the substrate. The inefficiency of the technique is due to the metal coating that is deposited onto the rest of the vacuum chamber at the same time. Only a small percentage of the metal that is consumed by the process lands on the substrate, with the rest being lost.
Electroplating would seem to be the proper candidate for metallizing diamond film with gold. With electroplating, the plated metal is applied directly to the target, resulting in much less waste as compared to physical vapor deposition. However, even though electroplating has established itself as a workhorse technology for cost effective thin film and foil fabrication in the electronics industry, only sputtering and evaporation of gold and copper have so far been commercially successfully utilized in metallizing diamond film substrates (and only on small substrates and only to small thicknesses).
"Metallizing CVD Diamond For Electronic Applications", Iacovangelo et al. International Journal of Microelectronics And Electronics Packaging, Vol. 17, No. 3, at 252-258 (1994), discloses a physical vapor deposition technique for depositing a gold layer onto a diamond film. As disclosed by Iacovangelo et al., thin gold films are applied to metal seed layers on diamond films by either a sputtering process or a chemical vapor deposition process.
As shown for coat numbers 11-13, the gold layers applied by the teachings of Iacovangelo et al. exhibit adhesion to the diamond substrate on the order of 4 to 10 Kpsi. Unfortunately, the gold layers produced by Iacovangelo et al were on the order of 0.5 microns thin, too thin for use in most applications.
Iacovangelo et al., further disclose the electroplating of a triple layer of copper, nickel and then gold onto a patterned thin film. However, as shown in FIG. 4 of Iacovangelo et al., this electroplated layer is on the order of 200 .mu.m wide, far too narrow for many applications. Electroplating onto diamond film substrates on the order of 1 cm.times.1 cm or larger requires that the problems induced by thermal stress be solved.
Iacovangelo et al. do not disclose or teach how to electroplate onto larger diamond film substrates in a manner sufficient to overcome the problems induced by thermal stress. Biaxial stresses increase with increasing diamond film size.
Additional problems with applying metal layers to diamond films include blistering, peeling and delamination.
Therefore, there is a need in the art for a process for metallizing diamond and other types of substrates which does not suffer from one or more of the prior art limitations.
There is another need in the art for an electroplating process for metallizing diamond and other types of substrates which does not suffer from one or more of the prior art limitations.
There is even another need in the art for an electroplating process for metallizing diamond and other types of substrates which provides a product with suitable adhesion between the gold layer and the diamond film.
There is still another need in the art for an electroplating process for metallizing diamond and other types of substrates which provides a product with suitable surface roughness.
There is yet another a need in the art for metallized diamond and other types of substrates which do not suffer from the prior art limitations.
There is even still another need in the art for a metallized diamond and other types of substrates with suitable adhesion between the gold layer and the diamond film.
There is even yet another need in the art for a metallized diamond and other types of substrates with suitable surface roughness.
These and other needs in the art will become apparent to those of skill in the art upon review of this specification.